Protein compositions of venoms of South-American stinging ants, Ectatomma tuberculatum, Paraponera clavata (subfamily Ponerinae), and "tangarana" were analyzed. The venom of E. tuberculatum displayed the most complex protein composition (more than 15 polypeptides). The water-soluble fraction of the venoms of P. clavata and "tangarana" contained acidic proteins (pI < 3.5 to 5.2), whereas the venom of E. tuberculatum contained predominantly basic proteins (pI 8 to > 9.5). N-Terminal residues and N-terminal sequences of a number of polypeptides were determined. High-molecular-mass polypeptides of the P. clavata venom slightly stimulated the ATPase activity of mitochondrial F1-ATPase. Low-molecular-mass nonprotein components of this venom significantly inhibited the ATPase activity of submitochondrial particles and F1-ATPase from bovine heart mitochondria. The venoms of E. tuberculatum and "tangarana" produced no effect on the ATPase activity.